The present invention relates to apparatus that a person can wear during walking to apply an electrical stimulus to his or her body and particularly, though not exclusively to his or her leg.
The present invention provides apparatus for applying an electrical stimulus to a person""s leg in timed relationship to leg movement during walking in order to achieve a benefit.
For example, a person who has a dropped foot is unable to lift his or her toes clear of the ground during the swing phase of walking. Such a problem is seen in people who have either a peripheral nerve lesion, as a result of trauma or disease, or an upper motor neuron lesion. It is the latter that responds to neuromuscular stimulation. Lesions of the lower motor neurons result in destruction of the neural pathway so that muscle contraction can be achieved only through direct stimulation of the muscle fibers.
The first reference to functional electrical stimulation (FES) is the work by Liberson et al, xe2x80x9cFunctional electrotherapy in stimulation of the peroneal nerve synchronized with the swing phase of gait of hemiplegic patientsxe2x80x9d, Arch Phys. Med. rehabil 42, 202-205 (1961). At this time electrotherapy was commonplace, but functional electrotherapy was a new concept. Liberson defined it as follows: xe2x80x98. . . to provide the muscles with electrical stimulation so that at the very time of the stimulation the muscle contraction has a functional purpose, either in locomotion or in prehension or in other muscle activity. In other words, functional electrotherapy is a form of replacement therapy in cases where impulses coming from the central nervous system are lacking.xe2x80x99
Liberson used a portable stimulator to correct drop foot during walking. A train of pulses of 20-250 xcexcsec duration, frequency 30-100 Hz and maximum peak current 90 mA was applied through conductive rubber electrodes. The negative (active) electrode was placed over the common peroneal nerve below the knee and the large indifferent electrode either on the thigh or on the lower leg. The stimulator was worn in the pocket and a heel switch was used to trigger the stimulus during the swing phase of the gait cycle. The switch was worn on the shoe on the affected side so that the electrical circuit was interrupted during the stance phase, when the weight was on the heel, and allowed to flow when the heel was lifted during the swing phase. Liberson was enthusiastic about the results, reporting that all the subjects experienced considerable improvement in gait. Despite improvements in the apparatus used, the basic idea of FES has remained unchanged. Sixteen papers on the topic published in the period 1960-1977 have been reviewed by J. H. Burridge et al, Reviews in Clinical Gerontology, 8, 155-161 (1998).
U.S. Pat. No. 5,643,332 (Stein) is also concerned with FES and explains that although variants of the technique have been tried and some success has been obtained, the most common appliance fitted to people with foot drop is an ankle-foot orthosis (AFO) which is a plastics brace that fits around the lower leg and holds the foot at close to a 90xc2x0 angle with respect to the long axis of the leg, and which does not employ electrical stimulation. Stein gives a number of reasons why FES had not replaced the AFO, amongst which is unrehability of the foot switch. In order to overcome this problem, Stein proposes a tilt sensor for measuring the angular position of the lower leg, although he also provides a socket for a hand or foot switch for those patients who cannot use a tilt sensor as there is insufficient tilt of the lower leg. A muscle stimulator for knee stabilization, also based on a tilt switch, is disclosed in U.S. Pat. No. 4,796,631 (Grigoryev). Muscle stimulation for the treatment and prevention of venous thrombosis and pulmonary embolism is disclosed in U.S. Pat. No. 5,358,513 (Powell III).
Footwear with flashing lights controlled by pressure switches is known, see U.S. Pat. Nos. 5,546,681, 5,746,499 and 6,017,128 (L.A. Gear, Inc.), U.S. Pat. No. 5,903,103 (Gamer) and U.S. Pat. No. 6,104,140 (Wut).
It is an object of the invention to provide a stimulator controlled by a foot switch that is more reliable in use and therefore commands wider acceptance by users.
It is also an object of the invention to provide a circuit for triggering by a pressure switch subject to repeated use and/or adverse environmental conditions which adapts to changes of switch characteristics with time.
The invention provides a functional electrical stimulator for attachment to the lower leg comprising;
first and second electrodes for attachment to the leg to apply an electrical stimulus;
a foot switch for sensing foot rise or foot strike;
a circuit responsive to said foot switch for generating stimulation pulses; and
means forming part of said circuit for responding to changes in the resistance characteristics of said switch means by adjusting a corresponding response threshold of said circuit.
The electrodes and the Coot switch are removably connected by e.g. plug and socket connectors to a body of the apparatus in which batteries and an electrical control circuit are housed. The invention also covers the control circuit without the electrodes and foot switch in place. Thus the invention further provides electrical apparatus for connection as part of a functional electrical stimulator for a leg, said apparatus comprising:
means providing a removable connection for first and second electrodes that in use are attached to the leg to apply an electrical stimulus;
means providing a removable connection for a foot switch for sensing foot rise or foot strike;
a circuit for responding to said foot switch for generating stimulation pulses; and
means forming part of said circuit for responding to changes in the resistance characteristics of said switch by adjusting a corresponding response threshold of said circuit.
The invention also provides an electrical stimulator for attachment to the body comprising:
first and second electrodes for attachment to the body to apply an electrical stimulus;
switch means which passes between on and off states on application and removal of load;
a circuit responsive to said switch means for generating stimulation pulses; and
means forming part of said circuit for responding to changes in the resistance characteristics of said switch means by adjusting a corresponding response threshold of said circuit.
It is a further object of the invention to provide electrical stimulation apparatus that may be applied to the body to achieve effective control of discrete muscle groups.
In the case of a single channel stimulator, for example, that is used to control dropped foot problems remain in some users that control of the ankle, knee or hip joint may be desirable. Lack of knee flexion on swing through can give difficulty in ground clearance despite adequate dorsiflexion. Lack of plantar flexion and hip extension control prevents the acceleration effect of the terminal stance phase of gait. Quadriceps weakness can cause rapid fatigue, reducing the distance that users can walk. Lack of hip abduction due to poor control ofd the gluteus medialis can lead to a scissirs gait. Balance while walking can be significantly reduced by the absence of contra-lateral arm swing.
The above problems can be addressed, according to the invention, by stimuation of a selected second group of muscles at appropriate times duing the gait cycle.
In one aspect the invention provides an electrical stimulator for attachment to the body comprising:
first and second channels for supplying stimuli to discrete muscle groups, each channel having first and second electrodes for attachment to the body to apply an electrical stimulus to a respective muscle group aid a circuit for supplying stimulation pulses to said electrodes;
at least one switch means responsive to limb position for controlling the supply of stimulation pulses in at least one channel; and
means defining a signal pathway between the first and second channels so that the supply of stimulation pulses in one of said first and second channels can be controlled by the state of switch means associated with the other of said first and second channels. In the above stimulator, supply of the stimulation pulses via the first channel may be arranged to be initiated by change in state of a switch associated with the second channel and is arranged to be ended by change in state of a switch associated with the first channel.
A further form of the invention provides an electrical stimulator for attachment to the body comprising:
first and second channels for supplying stimuli to discrete muscle groups, each channel having first and second electrodes for attachment to the body to apply an electrical stimulus to a respective muscle group and a circuit for supplying stimulation pulses to said electrodes;
at least one switch means responsive to limb position for controlling the supply of stimulation pulses in at least one channel; and
means defining a signal pathway between the first and second channels so that the supply of stimulation pulses in one of said first and second channels can be controlled by the state of activity of the other of said first and second channels. In the above stimulator, change in state of switch means associated with the first channel may be arranged to initiate supply of the stimulation pulses in the first channel, and the signal pathway between the channels may include delay means so that supply of pulses in the first channel initiates supply of pulses in the second channel with a delay.
In a yet further form of the invention, an electrical stimulator for attachment to the body is provided that comprises:
first and second channels for supplying stimuli to discrete muscle groups, each channel having first and second electrodes for attachment to the body to apply an electrical stimulus to a respective muscle group and a circuit for supplying stimulation pulses to said electrodes; at least one switch means responsive to limb position for controlling the supply of stimulation pulses in at least one channel; and
means for controlling the supply of stimulation pulses in the second channel, said means being selected from (a) second switch means which changes state on the application of pressure and (b) connections to the first channel for supplying to said second channel a signal indicative of the state of the first channel.
Another alternative form of the invention provides an electrical stimulator for attachment to the body comprising:
first and second channels for supplying stimuli to discrete muscle groups, each channel having first and second electrodes for attachment to the body to apply an electrical stimulus to a respective muscle group and a circuit for supplying stimulation pulses to said electrodes;
at least one switch means responsive to limb position for controlling the supply of stimulation pulses in at least one channel;
the first channel having means arranged to cause the stimulation pulses to time-out after a predetermined period and the second channel having no or disabled timing means so that supply of stimulation pulses is continuous in a predetermined state of limb position responsive switch means associated with that channel.
The above apparatus may take the form of a two-channel stimulator in order to address the problem of dropped foot and stimulate a further muscle group, e.g. the gluteus maximus, calf muscle or hamstring. Trials have shown that walking speed and physiological cost index are improved when either calf or hamstrings are stimulated in addition to common peroneal stimulation. The apparatus may also be used to treat bilateral dropped foot.
The invention also provides methods for the treatment of patients using the above two-channel apparatus.
In a further aspect the invention provides a pressure-sensitive resistor useable as a foot switch to be located in, on or under a shoe insole, said switch having an active portion comprising an array of fingers in contact with a conductive pad so that mechanical pressure urging the pad towards the fingers reduces the resistance of the switch, the fingers being of a first conductive material and having leads also of said first conductive material, said leads being covered by a second conductive material.
The invention also provides in combination the above mentioned stimulation apparatus and the above mentioned pressure switch.